Superregenerative receiver



April 20, 1954 J. M. SCHMIDT ETAL SUPERREGENERATIVE RECEIVER Filed July 30, 1951 Jqhon Machiel Schmidt Johannes Jocobus' Zoclberg Von Zels'r Aer-1m Patented Apr. 20, 1954 Johan Machiel Schmidt and. Johannes Zelst; Eindhoven, Netherlandsr Zaalberg' van Jacohus.

assignorsto "Hartford National Bank and-- Trust- Company, Hartford, Conm, as trustee 7 Application July 30, 1951, SeriaLNo..239,262-

Claimspriority, application Netherlands August 23, 1950' 1 Thei inventionr r lates: to? supcrr eenerative-re ceiversi. Such: receivers-1 are! known to havea discharge; tuberoperatingaas. ani'oscillatcr; whose frequency is; determined by; the input. signal circuit. andwh se damning svvariedfby'a sor-(ial'led. quenching; oscillatiomin; a manner such that: for a;1portion of the-quenching oscillation period, the; amplitude of thesoscillations across; the circuitwillincrease froma definitedow initial value varying with the stren th 015- hessignalz to be received to; a definite final value; and rapidly drop again to theinitial value for the remaining portion-of this period.; Thcvoperation -is based on the, fact that theflnal, valuerofj the highsfrequency voltage across; the circuit; varies: withthe value of the initialvoltagci 'Ilhaheginning of th -time during Which; the voltage increases is the moment at which the;- circuit arrangement, is sensitive This mas/ he termed; the sensitivity mo ment.v Apart from thenoise voltagecnly- 31,551 nalgvoltage -is-toi prevail at: this moment across the circuit,

As usual;v thetubemay comprise acathode, an anode and a control-grid; ;a.circuittuned to the incoming frequency, and responsive to an incoming; signal is connected between the; cathode and the: controlsgrid, the anode; circuit being coupled withthe grid circuitin-atmannersuchthat positive, feed-back occurs, so that: a, negative damping effect isiproduced across the circuit-J and the; am-

plitude of theoscillationsacross thiscircui-t isvincreased; It, is also-common. practicata interrupt, or strongly. reduce, periodically thetanode current through-the action, of the quenchingoscillation, so that for the: quenchingnperiod the oscillation amplitude decreases owing. to the natural damping of. the circuit. Itis knownitoiintroducehereansadditicnal dampin for: example, with the u e of a second tube, which is negatively coupled back, 7

It has. furthermore been. suggested to, use

oscillator tubes. p ratin n. the cdynatront p iniple, ,Qr, magnetrons inv superregenerative receivers,

In order to ensure a satisfactory amplification in superregenerative receivers; the-amplitude of theoscillation is to increase by" approximately a factor 10 and decrease again in a single cycle of the quenching oscillation, which is composed of a negative damping period'and a positive damping period. The-quenching period is to be solong that at the-end of the positivedamping period theoscillations may: have dropped below the noist level. The-required amountof= positive I or negative circuit' damping-must ibesumcient to increase or 3 Claims; (Cl. 250-20) decrease-theosci-llation amplitude within a sum ciently short time: On the-other hand, in: all devices-of this kind; the frequency of the quench ing oscillation must-be high relative to the highest modulation frequency of the oscillationsto be received. It may be inferred therefrom that the band width of the circuit" is to be approximately ten times the-maximum modulation frequency;

In. the'known circuit-arrangements the decrease in damping (tithe-input oscillation circuit at the beg-inning of that part'of' the quenching period in which the. amplitude: of-the oscillations increases isgenerallyaccompanied'with a comparatively large; variation of" the anode: current of the tube, thus causing the negative damping. It has been found? that this variation of'the anode current: causes an interfering switchingon, phenomenon; The abrupt variation of the anode current produces: a: voltage pulse across the: input.oscillatiorrwcircuit, so that oscillations are; produced which will" interferewith proper circuit operation: iitheir amplitude corresponds with the signal amplitude across the circuit at the beginning of; the negative damping period; Ihis-eiiect interalia prevents longer waves vfrom beingreceived with-adequate. sensitivity.

In, other circ,v.-it..-arrangements;- in which the damping is not produced throughthe cut-off or the; reduction: of theranode: current; current variations are produced which give rise to: similar effects. The amplitude: of" all these interfering oscillations willzincreasewith, increasing quenchingrfrequency; and the: impedance of the circuit will. be--- increasedx accordingly: Consequently, superregenerative radio reception with longer waves of; for example; over mum, is nov longer possible; as due to the: increased circuitimpedia nce the usual. quenching; interruption frequency of; for example; 3Q',0\O0;C;/S'; wi11t produce strong intcrferencezpulsesi.

The-object of: the; invention is to provide aareceivergof thevkind doscribedin the preamble, in which the said; switching-om phenomenon is re.- ducedrtoa have; a negligible. effect. Therefore, this-newreceiver will beadapted totherecept-ion of osciilations :of longerwavelength; for example, ofimorethan1001mmv Since, for-the same reason, it'is possible to: choose aconsiderablyhigher quenching frequency in the inventors circuitarrangement than in the known circuit-arrangemerits; the new receiver is at the same time suitable for the reception of high frequency oscillations, which are modulated in WVBIYf-Wldfi ire.- quency-rangeysuclras used-in television;

With

inafter this positive damping is again obviated at the beginning of the oscillation period without producing an appreciable voltage pulse across the input oscillation circuit. It is thus ensured that no switching-on phenomenon occurs at the sensitivity moment. 7 7 I In this case one or more rectifiers which are periodically brought into a non-rectifying stateunder the action of the interruption frequency are preferably connected in parallel with the circuit. I It should be noted here that it is known to increase thedamping'of the input oscillation circuit in super-regenerative receivers during the time in which the oscillation is to be reduced, with the use of a rectifier connected in parallel with circuit; however, it has not been recognized that an abrupt variationcf current may produce interfering phenomena, while at the same time a variation of the anode current or of a direct current passing through the rectifier occurs. In super-regenerative receivers comprising a magnetron as the oscillator it has furthermore :been suggested to produce the damping by means of a discharge tube comprising a control-grid across which the quenching frequency is operative. In this case, a variation of the direct current passing through the latter tube occurs at the beginning' of the oscillation period.

In a superregenerative receiver it is furthermore known to connect two. tubes in the input oscillation circuit in push-pull so that the anode circuits act in parallel on the load. In'this case. however, one tube exclusively serves for producing damping for the other. Since the quenching oscillation is supplied in phase opposition to the tubes, the total direct current component of the anode current may be regulated to vary only slightly. However, in this manner it is not pos sible to eliminate the aforesaid switching-on phenomenon as this would require an adjustment of the currents so accurate as to be unobtainable in practice. 1

In order that the invention may be more clearly understood and readily carried into effect, it'will now be described more fully with reference to the accompanying drawing, in which Fig. 1

and 2 show alternative embodiments of the invention and in which Figs. 3, 4 and 5 are graphs which aid in the explanation of the invention.

Fig. 1 shows a circuit-arrangement comprising a single tube operating as a superregenerative detector, shown here as a triode'for the sake of simplicity. The oscillations coming from the .aerial'are inductively supplied to the input'oscillation circuit comprising an inductance 2 and a variable capacitor 3. This circuit is grounded at one end and connected at the other end through ,a capacitor 4 to the control-grid of a tube 5. The anode of the latter is connected through a feedback coil 1 coupled with the inductance 2 and through a resistor 8 to the positive terminal of thecurrent supply. The modulation oscillations are taken from terminals 9. The grid of the tube is grounded through a leak resistor 6.

The feedback is such that it produces across the circuit l spontaneous oscillations which are periodically quenched in accordance with the superregenerative principle. According to the invention, this is effected in the circuit-arrange ment shown by connecting in parallel with the circuit the series combination of a resistor I I and a rectifier l2. To the terminals ll) of the resistor II is connected at quenching frequency generator The characteristic curve of the latter is approximately a rectangular wave.

As is indicated in Fig. 3 by the broken line, the leading edges of the voltage Waves are slightly rounded off; the horizontal line of Fig. 3 indicates the zero line at which no bias voltage is operative across the rectifier l2. The rectifier 12 operates as avirtual rectifier, which only rec- .tifies the positive halves of each cycle of the highfrequency voltage operative across circuit 2, 3. At the time of such rectification the circuit is damped to such an extent that the oscillations produced across it by the oscillator tube rapidly decrease in amplitude to a'very low value. If during the occurrence of a positive voltage pulse the upper terminal I0 becomes positive, the rectifying action abruptly ceases, which, however, is not attended. by a variation of the direct current component across the circuit. The damping of the circuit 2, 3 due to the rectifier action is eliminated so that the oscillations across this circuit can increase. At theend of the positive voltage pulse the voltage at the upper terminal Hl becomes again equal to that of the lower terminal, and the oscillations produced by the oscillator tube again vanish rapidly. The gradual increase of the positive voltage at the upper ter minal is intended to avoid a current pulse across the capacitance of the rectifier. The reduction of the voltage at the upper terminal to zero may be comparativelyabrupt without adversely affecting the circuit, since, at the instant when the damping oc'curs,'the' oscillations'across the circuit have so large an amplitude, with respect to whatever oscillations which may be produced by current pulses due to this reduction that the circuit is relatively unaffected.

The wave form'of the quenching interruption oscillation need not be rectangular; as an alternative; this voltage may be composed of a sine voltage superposed on a direct voltage, which is approximately equal to the maximum value of the sine voltage, as is shown in Fig. 4. As a further alternative, use may be made of a saw-tooth voltage preferably having a steep trailing edge (Fig. 5). However, inall cases the voltage should be such that the rectifier cannot carry an appreciable direct current component.

The rectifier I2 should preferably have a sharply bentover characteristic curve, so that it will have a low internal resistance at a low amplitude of the high-frequency oscillations in, the circuit. The maximum value of the resistor, H is set by the requirement that the parallel com bination l I, I2 should exert a strong damping influence on the circuit 2, 3. This requirement also. determines the-resistance of the rectifier i2 in rectifying condition.

If the rectifier l2 has excessive capacitance when a positive voltage pulse is produced at the upper terminal of the resistor H, the resultant charge current may cause a switching-on phenomenon which poduces interfering oscillations. Consequently, this capacitance should be low, for example lower than 1 micro-microfarad. It has been found that for the purpose of the invention.

scel d e iifie s ra t cglalt r W able, although normal diodes may also yield satisfactory results. Germanium rectifiers are very suitable, since they have not only a low capacitance but can also resist comparatively high voltages, for example, 50 v. and upwards. This is or importance since the cut-01f voltage of the rectifier is to be higher than the maximum amplitude of the high-frequency oscillation in the circuit. The latter voltage may, for example, be of the order of v.

Since the anode current of the tube remains constant and other variations of the direct current do not occur in the circuits when a positive voltage pulse occurs, the aforesaid switching-on phenomenon does not occur. It has been found that thus the waves in the range from 230 to 660 meters can be received with satisfactory results.

Fig. 2 shows a circuit-arrangement, in which use is made of a push-pull combination of two discharge tubes l5 and It. In this case the oscillation circuit is connected between the anodes of the tubes; the circuit inductance It is provided with a central tap. The anode circuit furthermore comprises the resistor 8, from the lower end of which the modulation voltage is taken at the terminals 0.

Because of the connection of the anode of tube 65 through a capacitor it to the grid of tube :6, and the connection of the anode of tube 16 through a capacitor I! to the grid of tube i6, oscillations are produced in tubes and i6. Leak resistors 18 and 20 are provided between the grids and the interconnected cathodes.

Furthermore, two rectifiers 2i and 22, preferably germanium rectifiers, are connected, in opposite sense, in parallel with the circuit 3, is. The junction of these rectifiers is connected through a resistor H to the central tap on the coil M. Ihe quenching oscillation is supplied through terminals to resistor M. This quenching oscillation has such a Wave form that a direct current component cannot pass through the rectifier.

The operation or the circuit-arrangement shown in Fig. 2 is otherwise identical with that of the circuit-arrangement shown in Fig. 1.

The rectifiers may be replaced by other elements, for example, controlled discharge tubes, by means of which the circuit is short-circuited or strongly damped during the damping period. The short-circuit may even be carried out with the use of a mechanical switch. This may be of importance for measuring purposes, if the frequencies are very low. However, care should be taken that no strong direct-current variations occur at the beginning of the negative damping period.

What we claim is:

1. In a superregenerative receiver wherein an incoming signal is regenerated and periodically quenched by a quenching oscillation, the combination comprising a pair of electron discharge tubes each having a cathode, a control grid and an anode, a push-pull resonant circuit tuned to said incoming signal and including a centertapped inductor connected between the anodes of said tubes, means to cross-couple the grids and anodes of said tubes to effect regeneration, means to apply an operating potential for said tubes between the cathodes thereof and the center-tap of said inductor, a pair of unidirectionally conductive devices, a damping resistance for said resonant circuit having one end connected to said center-tap and having the other end connected in one direction through one of said devices to the anode of one tube and connected in the other direction through the other of said devices to the anode of the other tube, and means to apply the quenching oscillation across said damping resistance.

2. In a superregenerative receiver wherein an incoming signal is regenerated and periodically quenched by a quenching oscillation, the device comprising a pair of electron discharge tubes each having a cathode, a control grid and an anode, a push-qoull resonant circuit tuned to said incoming signal and including a center-tapped inductor connected between the anodes of said tubes, means to cross-couple the grids and anodes of said tubes to effect regeneration, means to apply an operating potential for said tubes between the cathodes thereof and the center-tap of said inductor, a pair of rectifiers, a damping resistance for said resonant circuit having one end connected to said center-tap and having the other end connected in one sense through one of said rectifiers to the anode of one tube and connected in the other sense through the other or said rectifiers to the anode of the other tube, and means to apply the quenching oscillation across said damping resistance.

3. In a superregenerative receiver wherein an incoming signal is regenerated and periodically quenched by a quenching oscillation, the device comprising a pair of electron discharge tubes each having a cathode, a control grid and an anode, a push-pull resonant circuit tuned to'said incoming signal and including a center-tapped inductor connected between the anodes of said tubes and a variable condenser connected across said inductor, capacitive means to cross-couple the grids and anodes of said tubes to eflect regeneration, means to apply an operating potential for said tubes between the cathodes thereof and the center-tap of said inductor, a pair of germanium diodes, a damping resistance for said resonant circuit having one end connected to said center-tap and having the other end connected in one sense through one of said diodes to the anode of one tube and connected in the other sense through the other or said diodes to the anode of the other tube, means to apply the quenching oscillation across said damping resistance, and means coupled between said center-tap and said cathodes to obtain an output voltage.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,044,061 Crawford June 16, 1936 2,412,710 Bradley Dec. 17, 1946 2,553,219 Tellier May 15, 1951 

